The present invention relates to a novel fluoroelastomer composition, and more particularly to a fluoroelastomer composition containing a fluoroelastomer having stabilized end group which can be cured with an appropriate induction time and a satisfactory fast cure rate by the use of a specific curing agent system.
Fluoroelastomer, for instance, elastomeric copolymers of vinylidene fluoride and other copolymerizable fluorine-containing monomers, such as vinylidene fluoridehexafluoropropene copolymer and vinylidene fluoride-hexafluoropropene-tetrafluoroethylene terpolymer, are well known in the art. These fluoroelastomer can be cured by using a diamine or an organic peroxide, or a combination of an aromatic polyhydroxy compound and an appropriate accelerator, and their vulcanizates, namely fluoro-rubbers, have excellent resistances to heat, oils, solvents and chemical reagents. In general, from the viewpoint of an economical advantage on manufacture, they have prepared by inorganic free-radical catalyzed polymerization of the monomers in an aqueous medium, for instance, employing an initiator comprising an inorganic peroxide such as ammonium persulfate. The inorganic free-radical initiator gives a polymer having ionic end groups such as --COOH and --OSO.sub.3 H, or their salts.
The proportion of ionic end groups in the polymer is reduced when the inorganic free-radical catalyzed polymerization is carried out in the presence of an isoparaffin. This process provides fluoroelastomers having ionic end groups mentioned above and nonionic end groups derived from the isoparaffin. For instance, when isopentane is employed as the isoparaffin, it is assumed that the nonionic end groups are, for example, such as --H and --C(CH.sub.3).sub.2 CH.sub.2 CH.sub.3. The fluoroelastomers so prepared have good processing characteristics and provide vulcanizates with excellent compression set properties. However, such fluoroelastomers have certain disadvantages. Thus, for instance, when such fluoroelastomers are cured by using a diamine curing agent which has been the most widely employed in the art, the cure rate is slow and, therefore, the curing time is long.